Brake pad wear detection system

Abstract

A brake pad wear detection system comprises a brake having a brake pad and a conductive braking face, the brake pad and the conductive braking face engaging during braking. A sensor loop is embedded in the brake pad and positioned to be broken when the wear to the brake pad exceeds the working limit. An indicator means and a detecting means for operating the indicator means are provided, the detecting means detecting contact between the sensor loop and the braking face as well as breakage of the sensor loop.

I claim: 
     
       1. A brake pad wear detection system comprising a brake having a brake pad and a conductive braking face, the brake pad and the conductive braking face engaging during braking, a voltage supply line, an earth line, a first impedance means one end of which is connected to the voltage supply line, a second impedance means one end of which is connected to the earth line, a sensor loop connected in series between the first and second impedance means and embedded in the brake pad and positioned so as to be broken when the wear to the pad exceeds the working limit, indicator means and means connected to the common point of the first impedance means and the sensor loop for detecting if the potential at said common point is between first and second predetermined voltages, the detecting means operating the indicator means upon contact between the braking face and the sensor loop and also upon breakage of the sensor loop. 
     
     
       2. A detection system as claimed in claim 1 in which the indicator means comprises a single lamp which is energised temporarily during contact between the braking face and the sensor loop, and permanently upon breakage of the sensor loop. 
     
     
       3. A detection system as claimed in claim 1 or 2 in which the detecting means includes a first comparator for comparing the potential at said common point with the first predetermined voltage and a second comparator for comparing the potential at said common point with the second predetermined voltage. 
     
     
       4. A detection system as claimed in claim 1 or 2 in which the first impedance means comprises a first resistor and the second impedance means comprises a second resistor and in which the detecting means includes a zener diode and a third resistor connected in series between said common point and the earth line, a first transistor, the emitter of which is connected to the earth line and the base of which is connected to the common point of the zener diode and the third resistor, and a second transistor, the emitter of which is connected to the earth line and the base of which is connected to the collector of the first transistor and through a fourth resistor to the common point of said first resistor and the sensor loop, the indicator means being controlled by the second transistor. 
     
     
       5. A detection system as claimed in claim 1 or 2 in which there are a plurality of brakes, each brake having an associated brake pad, conductive braking face and sensor loop embedded in the brake pad, the sensor loops being connected in series.